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  • 1. Feng, Xue
    et al.
    Ackerly, David D.
    Dawson, Todd E.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    McLaughlin, Blair
    Skelton, Robert P.
    Vico, Giulia
    Weitz, Andrew P.
    Thompson, Sally E.
    Beyond isohydricity: The role of environmental variability in determining plant drought responses2019Inngår i: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 42, nr 4, s. 1104-1111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the appeal of the iso/anisohydric framework for classifying plant drought responses, recent studies have shown that such classifications can be strongly affected by a plant's environment. Here, we present measured in situ drought responses to demonstrate that apparent isohydricity can be conflated with environmental conditions that vary over space and time. In particular, we (a) use data from an oak species (Quercus douglasii) during the 2012-2015 extreme drought in California to demonstrate how temporal and spatial variability in the environment can influence plant water potential dynamics, masking the role of traits; (b) explain how these environmental variations might arise from climatic, topographic, and edaphic variability; (c) illustrate, through a common garden thought experiment, how existing trait-based or response-based isohydricity metrics can be confounded by these environmental variations, leading to Type-1 (false positive) and Type-2 (false negative) errors; and (d) advocate for the use of model-based approaches for formulating alternate classification schemes. Building on recent insights from greenhouse and vineyard studies, we offer additional evidence across multiple field sites to demonstrate the importance of spatial and temporal drivers of plants' apparent isohydricity. This evidence challenges the use of isohydricity indices, per se, to characterize plant water relations at the global scale.

  • 2.
    Greiser, Caroline
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Hederová, Lucia
    Vico, Giulia
    Wild, Jan
    Macek, Martin
    Kopecký, Martin
    Higher soil moisture increases microclimate temperature buffering in temperate broadleaf forests2024Inngår i: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 345, artikkel-id 109828Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Forest canopies can buffer the understory against temperature extremes, often creating cooler microclimates during warm summer days compared to temperatures outside the forest. The buffering of maximum temperatures in the understory results from a combination of canopy shading and air cooling through soil water evaporation and plant transpiration. Therefore, buffering capacity of forests depends on canopy cover and soil moisture content, which are increasingly affected by more frequent and severe canopy disturbances and soil droughts. The extent to which this buffering will be maintained in future conditions is unclear due to the lack of understanding about the relationship between soil moisture and air temperature buffering in interaction with canopy cover and topographic settings. We explored how soil moisture variability affects temperature offsets between outside and inside the forest on a daily basis, using temperature and soil moisture data from 54 sites in temperate broadleaf forests in Central Europe over four climatically different summer seasons. Daily maximum temperatures in forest understories were on average 2 °C cooler than outside temperatures. The buffering of understory temperatures was more effective when soil moisture was higher, and the offsets were more sensitive to soil moisture on sites with drier soils and on sun-exposed slopes with high topographic heat load. Based on these results, the soil–water limitation to forest temperature buffering will become more prevalent under future warmer conditions and will likely lead to changes in understory communities. Thus, our results highlight the urgent need to include soil moisture in models and predictions of forest microclimate, understory biodiversity and tree regeneration, to provide a more precise estimate of the effects of climate change.

  • 3.
    Livsey, John
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Katterer, Thomas
    Vico, Giulia
    Lyon, Steve W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. The Nature Conservancy, USA..
    Lindborg, Regina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Scaini, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Da, Chau Thi
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Do alternative irrigation strategies for rice cultivation decrease water footprints at the cost of long-term soil health?2019Inngår i: Environmental Research Letters, E-ISSN 1748-9326, Vol. 14, nr 7, artikkel-id 074011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The availability of water is a growing concern for flooded rice production. As such, several water-saving irrigation practices have been developed to reduce water requirements. Alternate wetting and drying and mid-season drainage have been shown to potentially reduce water requirements while maintaining rice yields when compared to continuous flooding. With the removal of permanently anaerobic conditions during the growing season, water-saving irrigation can also reduce CO2 equivalent (CO2eq) emissions, helping reduce the impact of greenhouse gas (GHG) emissions. However, the long-term impact of water-saving irrigation on soil organic carbon (SOC)-used here as an indicator of soil health and fertility-has not been explored. We therefore conducted a meta-analysis to assess the effects of common water-saving irrigation practices (alternate wetting and drying and mid-season drainage) on (i) SOC, and (ii) GHG emissions. Despite an extensive literature search, only 12 studies were found containing data to constrain the soil C balance in both continuous flooding and water-saving irrigation plots, highlighting the still limited understanding of long-term impacts of water-saving irrigation on soil health and GHG emissions. Water-saving irrigation was found to reduce emissions of CH4 by 52.3% and increased those of CO2 by 44.8%. CO2eq emissions were thereby reduced by 18.6% but the soil-to-atmosphere carbon (C) flux increased by 25% when compared to continuous flooding. Water-saving irrigation was also found to have a negative effect on both SOC-reducing concentrations by 5.2%-and soil organic nitrogen-potentially depleting stocks by more than 100 kgN/ha per year. While negative effects of water-saving irrigation on rice yield may not be visible in short-term experiments, care should be taken when assessing the long-term sustainability of these irrigation practices because they can decrease soil fertility. Strategies need to be developed for assessing the more long-term effects of these irrigation practices by considering trade-offs between water savings and other ecosystem services.

  • 4. Luan, Xiangyu
    et al.
    Bommarco, Riccardo
    Scaini, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Vico, Giulia
    Combined heat and drought suppress rainfed maize and soybean yields and modify irrigation benefits in the USA2021Inngår i: Environmental Research Letters, E-ISSN 1748-9326, Vol. 16, nr 6, artikkel-id 064023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Heat and water stress can drastically reduce crop yields, particularly when they co-occur, but their combined effects and the mitigating potential of irrigation have not been simultaneously assessed at the regional scale. We quantified the combined effects of temperature and precipitation on county-level maize and soybean yields from irrigated and rainfed cropping in the USA in 1970–2010, and estimated the yield changes due to expected future changes in temperature and precipitation. We hypothesized that yield reductions would be induced jointly by water and heat stress during the growing season, caused by low total precipitation (PGS) and high mean temperatures (TGS) over the whole growing season, or by many consecutive dry days (CDDGS) and high mean temperature during such dry spells (TCDD) within the season. Whole growing season (TGS, PGS) and intra-seasonal climatic indices (TCDD, CDDGS) had comparable explanatory power. Rainfed maize and soybean yielded least under warm and dry conditions over the season, and with longer dry spells and higher dry spell temperature. Yields were lost faster by warming under dry conditions, and by lengthening dry spells under warm conditions. For whole season climatic indices, maize yield loss per degree increase in temperature was larger in wet compared with dry conditions, and the benefit of increased precipitation greater under cooler conditions. The reverse was true for soybean. An increase of 2 °C in TGS and no change in precipitation gave a predicted mean yield reduction across counties of 15.2% for maize and 27.6% for soybean. Irrigation alleviated both water and heat stresses, in maize even reverting the response to changes in temperature, but dependencies on temperature and precipitation remained. We provide carefully parameterized statistical models including interaction terms between temperature and precipitation to improve predictions of climate change effects on crop yield and context-dependent benefits of irrigation.

  • 5.
    Manzoni, Stefano
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Chakrawal, Arjun
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Fischer, Thomas
    Schimel, Joshua P.
    Porporato, Amilcare
    Vico, Giulia
    Rainfall intensification increases the contribution of rewetting pulses to soil heterotrophic respiration2020Inngår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, nr 15, s. 4007-4023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Soil drying and wetting cycles promote carbon (C) release through large heterotrophic respiration pulses at rewetting, known as the Birch effect. Empirical evidence shows that drier conditions before rewetting and larger changes in soil moisture at rewetting cause larger respiration pulses. Because soil moisture varies in response to rainfall, these respiration pulses also depend on the random timing and intensity of precipitation. In addition to rewetting pulses, heterotrophic respiration continues during soil drying, eventually ceasing when soils are too dry to sustain microbial activity. The importance of respiration pulses in contributing to the overall soil heterotrophic respiration flux has been demonstrated empirically, but no theoretical investigation has so far evaluated how the relative contribution of these pulses may change along climatic gradients or as precipitation regimes shift in a given location. To fill this gap, we start by assuming that heterotrophic respiration rates during soil drying and pulses at rewetting can be treated as random variables dependent on soil moisture fluctuations, and we develop a stochastic model for soil heterotrophic respiration rates that analytically links the statistical properties of respiration to those of precipitation. Model results show that both the mean rewetting pulse respiration and the mean respiration during drying increase with increasing mean precipitation. However, the contribution of respiration pulses to the total heterotrophic respiration increases with decreasing precipitation frequency and to a lesser degree with decreasing precipitation depth, leading to an overall higher contribution of respiration pulses under future more intermittent and intense precipitation. Specifically, higher rainfall intermittency at constant total rainfall can increase the contribution of respiration pulses up to similar to 10 % or 20 % of the total heterotrophic respiration in mineral and organic soils, respectively. Moreover, the variability of both components of soil heterotrophic respiration is also predicted to increase under these conditions. Therefore, with future more intermittent precipitation, respiration pulses and the associated nutrient release will intensify and become more variable, contributing more to soil biogeochemical cycling.

  • 6.
    Manzoni, Stefano
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Swedish University of Agricultural Sciences, Sweden.
    Vico, Giulia
    Katul, Gabriel
    Palmroth, Sari
    Porporato, Amilcare
    Optimal plant water-use strategies under stochastic rainfall2014Inngår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, nr 7, s. 5379-5394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants with a balanced hydraulic system that protects them from cavitation while allowing an efficient transport of water necessary for photosynthesis. In particular, observations suggest correlations between the water potentials at which xylem cavitation impairs water movement and the one at stomatal closure, and between maximum xylem and stomatal conductances, begging the question as to whether such coordination emerges as an optimal water-use strategy under unpredictable rainfall. Here mean transpiration <E> is used as a proxy for long-term plant fitness and its variations as a function of the water potentials at 50% loss of stem conductivity due to cavitation and at 90% stomatal closure are explored. It is shown that coordination between these hydraulic traits is necessary to maximize <E>, with rainfall patterns altering the optimal range of trait values. In contrast, coordination between ecosystem-level conductances appears not necessary to maximize <E>. The optimal trait ranges are wider under drier than under mesic conditions, suggesting that in semiarid systems different water use strategies may be equally successful. Comparison with observations across species from a range of ecosystems confirms model predictions, indicating that the coordinated functioning of plant organs might indeed emerge from an optimal response to rainfall variability.

  • 7.
    Messori, Gabriele
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Uppsala University, Sweden.
    Ruiz-Pérez, Guiomar
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish University of Agricultural Sciences (SLU), Sweden.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Vico, G.
    Climate drivers of the terrestrial carbon cycle variability in Europe2019Inngår i: Environmental Research Letters, E-ISSN 1748-9326, Vol. 14, nr 6, artikkel-id 063001Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The terrestrial biosphere is a key component of the global carbon cycle and is heavily influenced by climate. Climate variability can be diagnosed through metrics ranging from individual environmental variables, to collections of variables, to the so-called climate modes of variability. Similarly, the impact of a given climate variation on the terrestrial carbon cycle can be described using several metrics, including vegetation indices, measures of ecosystem respiration and productivity and net biosphere-atmosphere fluxes. The wide range of temporal (from sub-daily to paleoclimatic) and spatial (from local to continental and global) scales involved requires a scale-dependent investigation of the interactions between the carbon cycle and climate. However, a comprehensive picture of the physical links and correlations between climate drivers and carbon cycle metrics at different scales remains elusive, framing the scope of this contribution. Here, we specifically explore how climate variability metrics (from single variables to complex indices) relate to the variability of the carbon cycle at sub-daily to interannual scales (i.e. excluding long-term trends). The focus is on the interactions most relevant to the European terrestrial carbon cycle. We underline the broad areas of agreement and disagreement in the literature, and conclude by outlining some existing knowledge gaps and by proposing avenues for improving our holistic understanding of the role of climate drivers in modulating the terrestrial carbon cycle.

  • 8. Mrad, Assaad
    et al.
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Oren, Ram
    Vico, Giulia
    Lindh, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Katul, Gabriel
    Recovering the Metabolic, Self-Thinning, and Constant Final Yield Rules in Mono-Specific Stands2020Inngår i: Frontiers in Forests and Global Change, E-ISSN 2624-893X, Vol. 3, artikkel-id UNSP 62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Competition among plants of the same species often results in power-law relations between measures of crowding, such as plant density, and average size, such as individual biomass. Yoda's self-thinning rule, the constant final yield rule, and metabolic scaling, all link individual plant biomass to plant density and are widely applied in crop, forest, and ecosystem management. These dictate how plant biomass increases with decreasing plant density following a given power-law exponent and a constant of proportionality. While the exponent has been proposed to be universal and thus independent of species, age, environmental, and edaphic conditions, different theoretical mechanisms yield absolute values ranging from less than 1 to nearly 2. Here, eight hypothetical mechanisms linking the exponent to constraints imposed on plant competition are featured and contrasted. Using dimensional considerations applied to plants growing isometrically, the predicted exponent is -3/2 (Yoda's rule). Other theories based on metabolic arguments and network transport predict an exponent of -4/3. These rules, which describe stand dynamics over time, differ from the rule of constant final yield that predicts an exponent of -1 between the initial planting density and the final yield attained across stands. The latter can be recovered from statistical arguments applied at the time scale in which the site carrying capacity is approached. Numerical models of plant competition produce plant biomass-density scaling relations with an exponent between -0.9 and -1.8 depending on the mechanism and strength of plant-plant interaction. These different mechanisms are framed here as a generic dynamical system describing the scaled-up carbon economy of all plants in an ecosystem subject to differing constraints. The implications of these mechanisms for forest management under a changing climate are discussed and recent research on the effects of changing aridity and site quality on self-thinning are highlighted.

  • 9. Vico, Giulia
    et al.
    Way, Danielle A.
    Hurry, Vaughan
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Can leaf net photosynthesis acclimate to rising and more variable temperatures?2019Inngår i: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 42, nr 6, s. 1913-1928Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Under future climates, leaf temperature (T-l) will be higher and more variable. This will affect plant carbon (C) balance because photosynthesis and respiration both respond to short-term (subdaily) fluctuations in T-l and acclimate in the longer term (days to months). This study asks the question: To what extent can the potential and speed of photosynthetic acclimation buffer leaf C gain from rising and increasing variable T-l? We quantified how increases in the mean and variability of growth temperature affect leaf performance (mean net CO2 assimilation rates, A(net); its variability; and time under near-optimal photosynthetic conditions), as mediated by thermal acclimation. To this aim, the probability distribution of A(net) was obtained by combining a probabilistic description of short- and long-term changes in T-l with data on A(net) responses to these changes, encompassing 75 genera and 111 species, including both C3 and C4 species. Our results show that (a) expected increases in T-l variability will decrease mean A(net) and increase its variability, whereas the effects of higher mean T-l depend on species and initial T-l, and (b) acclimation reduces the effects of leaf warming, maintaining A(net) at >80% of its maximum under most thermal regimes.

  • 10. Wu, Minchao
    et al.
    Vico, Giulia
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Cai, Zhanzhang
    Bassiouni, Maoya
    Tian, Feng
    Zhang, Jie
    Ye, Kunhui
    Messori, Gabriele
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Uppsala University, Sweden.
    Early Growing Season Anomalies in Vegetation Activity Determine the Large-Scale Climate-Vegetation Coupling in Europe2021Inngår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 126, nr 5, artikkel-id e2020JG006167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The climate-vegetation coupling exerts a strong control on terrestrial carbon budgets and will affect the future evolution of global climate under continued anthropogenic forcing. Nonetheless, the effects of climatic conditions on such coupling at specific times in the growing season remain poorly understood. We quantify the climate-vegetation coupling in Europe over 1982-2014 at multiple spatial and temporal scales, by decomposing sub-seasonal anomalies of vegetation greenness using a grid-wise definition of the growing season. We base our analysis on long-term vegetation indices (Normalized Difference Vegetation Index and two-band Enhanced Vegetation Index), growing conditions (including 2m temperature, downwards surface solar radiation, and root-zone soil moisture), and multiple teleconnection indices that reflect the large-scale climatic conditions over Europe. We find that the large-scale climate-vegetation coupling during the first two months of the growing season largely determines the full-year coupling. The North Atlantic Oscillation and Scandinavian Pattern phases one-to-two months before the start of the growing season are the dominant and contrasting drivers of the early growing season climate-vegetation coupling over large parts of boreal and temperate Europe. The East Atlantic Pattern several months in advance of the growing season exerts a strong control on the temperate belt and the Mediterranean region. The strong role of early growing season anomalies in vegetative activity within the growing season emphasizes the importance of a grid-wise definition of the growing season when studying the large-scale climate-vegetation coupling in Europe. Plain Language Summary Climate and terrestrial ecosystems interact and affect the global climate. Such a climate-vegetation relationship can be effectively quantified by using satellites to measure how leafy and active the vegetation is, and numerical indices reflecting large-scale climate patterns over a given region. Previous studies generally focused on changes in mean vegetation indices over the full growing season, which is usually defined by a fixed range of astronomical months for large geographical regions. This overlooks the fact that growing seasons differ in space and vegetation responds differently to the climate in different growing season periods. In this study, we explore how vegetation and climate interact within a growing season, here defined specifically for the local conditions. We find that there are strong relationships between the large-scale climate patterns and vegetation indices during the first two months of the growing season. Our findings highlight the important role of the vegetation activity during the early growing season for the year-to-year vegetation changes in Europe. Hence, for a better understanding of the climate-vegetation relationships, it is necessary to consider the spatial differences in the growing season, in particular for large geographical regions.

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